Method and apparatus for simultaneously producing large and small heat hardened agglomerates of mineral ore

ABSTRACT

A method and apparatus is disclosed for simultaneously producing heat hardened agglomerate balls of two size ranges from finely divided mineral ore. The apparatus includes a first balling device for making balls of ore in a first size range, an indurating furnace assembly for drying, preheating and heat hardening the balls, means for collecting a predetermined quantity of hardened balls of a size within the first size range, and a second balling device. According to the method disclosed the collected hardened balls are delivered to the second balling device and rolled in additional moistened ore to apply a coating thereto until the collected balls grow to a second size range. The coated balls are then fed to the furnace with the balls from the first balling device for drying, preheating and heat hardening the coating of the coated balls simultaneously with the drying, preheating and heat hardening of the first size range balls.

United States Paten Whitaker et al.

Feb. 4, 1 975 [75] Inventors: Orion C. Whitaker, Wauwatosa;

Glenn A. Heian, Franklin, both of Wis.

[73] Assignee: Allis-Chalmers Corporation,

Milwaukee, Wis.

[22]. Filed:' Oct. 1, 1973 [21] Appl. No.: 402,456

52 US. Cl. 75/3 [51] Int. Cl C21b 1/20 [58] Field of Search 75/3-5 [56]References Cited UNITED STATES PATENTS 2,l27,632 8/l938 Najarian 75/32,41 l,8'73 12/1946 Firth 7573 3,149,958 9/1964 Ward 75/3 X 3,l88,l956/1965 Price 75/3 X 3,333,951 8/1967 Ban 75/3 3,753,682 8/1973 Kohl 75/3Primary Examiner-Allen B. Curtis Attorney, Agent, or Firm-Arthur M.Streich [57] ABSTRACT livered to the second balling device and rolled inadditional moistened ore to apply a coating thereto until the collectedballs grow to a second size range. The coated balls are then fed to thefurnace with the balls from the first balling device for drying,preheating and heat hardening the coating of the coated ballssimultaneously with the drying, preheating and heat hardening of thefirst size range balls.

2 Claims, 1 Drawing Figure PATENTEUFEB 4mm 1 METHOD AND APPARATUS FORSIMULTANEOUSLY PRODUCING LARGE AND SMALL HEAT HARDENED AGGLOMERATES OFMINERAL ORE BACKGROUND OF THE INVENTION 1. Field of the Invention Thepresent invention relates to amethod and apparatus for agglomeratingfinely divided mineral ore and furnacing such agglomerates to produce ahard durable product. In particular the present invention relates toagglomerating and heat hardening such as iron oxide ores for subsequentconversion to the metals iron and steel.

2. Description of the Prior Art U.S. Pats. Nos. 2,750,272; 2,750,273 and2,750,274 of June 12, 1956, are examples of patents related to heathardening agglomerates of iron ore on a horizontal traveling grate.

U.S. Pats. Nos. 2,925,336 of Feb. 16, 1960; 3,313,534 of Apr. 11, 1967are examples of patents related to heat hardening agglomerates of oreutilizing both a horizontal traveling grate and a rotary kiln.

U.S. Pats. Nos. 3,301,659 of Jan. 31, 1967 and 3,319,949 of May 16, 1967are examples of patents related to rolling an unfired ball of mineralore in moist ore to produce a coated ball which is then fired'to hardenthe ball.

U.S. Pat. No. 2,127,632 of Aug. 23, 1938 relates to a ballof-metalliferous material having a nucleus or core which may be sinteredore.

I The present invention is directed to simultaneously producing desiredquantities ofheat hardened balls of 1 mineral ore in at least twodistinctly different size ranges, with balls of a first size being of asize usually produced according to the practices of the aforesaid priorart, and with balls of the second size also being produced which aresubstantially larger.

SUMMARY OF THE PRESENT INVENTION The present invention is directed toproducing substantial quantities of heat hardened balls of mineral ore,for example iron oxide ore, of standard size which usually falls withina range of three-eighths of an inch to five-eighths of an inch indiameter, for a use such as charging to a blast furnace. The presentinvention also provides for producing desired quantities of somewhatlarger heat hardened balls of perhaps three-fourths to 1% inches indiameter, for use as a coolant charge to a basic oxygen steelmakingfurnace and sometimes for charging a blast furnace as well.

When green ball diameters exceed five-eighths of an inch, induratingrates become heat-transfer and moisture-diffusion limited. That is, theindurating process, particularly on a grate, must be substantiallyslowed down to assure that all moisture is removed in drying beforepreheating and preheating must be prolonged to assure that requisitepreliminary induration occurs in the centers of the balls before theyare transferred into I a kiln for final heat hardening.

Further, experience has shown that even if this preheat ing balance isattained, the fire pellets may have underfired cores. Pellet quality isthen adversely affected.

The object of the present invention is to simultaneously produce fullyheat hardened balls of two sizes. one size of perhaps three-eighths ofan inch to fiveeighths of an inch in diameter and a larger size ofperhaps three-fourths of an inch to 1% inches in diameter.

According to a preferred embodiment of the present invention green ballsof finely divided mineral ore in a first preselected size range, perhapsthree-eighths of an inch to five-eighths of an inch, are made in aballing drum. The green balls of the first size are deposited on ahorizontal grate conveyer for drying, preferably by a down draft of hotgases, and preheating. The balls are then fired, preferably in a rotarykiln, until hard and abrasion resistant. The hardened first size ballspass a suitable device to collect a selected quantity of the balls fromthe total produced, and the collected balls are rolled in an additionalquantity of finely divided ore to apply a coating thereto until suchballs have grown in diameter to a second and larger preselected sizerange, perhaps three-fourths of an inch to 1% inches. The larger ballsare then deposited on top of the bed of smaller balls on the grate fordrying and preheating the coating ofthe large balls simultaneously withthe drying and preheating of the smaller balls. Both size balls are thentumbled through the rotary kiln for final hardening of the coating ofthe large balls and final hardening of the smaller balls. The fullyhardened balls of both sizes pass over the screening device to removethe large balls for their specialized use, and the smaller balls pass adevice to collect the preselected quantity of small balls for continuingthe coating operation while the remainder of the small size balls aredischarged for eventual use as such as blast furnace feed. The apparatusoperating according to the present method therefore continues tosimultaneously produce two sizes of heat hardened balls, and deliverseach size to its own conveyer.

Other features and objects of the present invention that have beenattained will appear from the more detailed description to follow withreference to an embodiment of the present invention shown in theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing showsdiagrammatically a side elevation, partly in section, of a balling andfurnacing system according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, suchas finely divided iron ore along with bentonite is discharged fromhopper l at a rate controlled by feeder 2, and mixed and rolled intosuitable agglomerates or balls 4 by such as a balling drum 5 which maybe of the type shown in US Pats. Nos. 1,994,718 and 2.41 1,873. Theballing drum 5 may be arranged to discharge to a vibrating screen 6having screen deck 7 with openings sized to screen out balls larger thanabout five-eighths of an inch diameter. Such oversize balls may bebroken by means (not shown) and recycled. Balls passing through deck 7pass over a screen deck 8 having openings to screen out balls smallerthan about three-eighths of an inch which, as shown, may be recycleddirectly to balling drum 5.

Balls passing through deck 7 but not through deck 8, of a size rangelarger than three-eighths of an inch but not larger than five-eighths ofan inch, are transferred by suitable conveying means and feeder 9 todischarge to a gas previous traveling grate l enclosed by a housing 11.The housing 11 has a baffle wall 12 projecting downwardly from the roofof housing 11 to a predetermined distance above the grate 10..The bafflewall 12 divides the space enclosed by housing 11 over grate 10 into adrying chamber 15 and a preheat chamber 16. Windboxes 17 and 18 arearranged beneath chambers 15 and 16. A chute 20 with a hood 21 connectsthe grate 10 to a rotary kiln 22. The kiln 22 has an axial burner 23.The kiln 22 may be mounted on rollers (not shown) for rotation in aconventional manner. A second chute 26 with a hood 27 that also servesas the firing hood for kiln 22, connects kiln 22 to a cooler 30 whichmay be an annular grate of the type shown in US. Pat. No. 2,256,017.

The agglomerates or balls 4 which are formed in balling drum are formedinto a bed on gr-ate 10, with individual agglomerates at rest relativeto each other, and the bed is transported by grate through the housing11 to the chute 20. At the chute 20 the bed of agglomerates is disruptedand the agglomerates are discharged into kiln 22. The agglomerates 4 aretumbled through the kiln 22 to the chute 26 which discharges theagglomerates as indurated pellets to the cooler 30.

A gas flow through kiln 22 proceeds counterflow to the movement of theagglomerates 4 through kiln 22. The gas flow'results'from air flowingfrom cooler 30 into kiln 22 and fuel and air admitted to kiln 22 throughthe axial burner 23. The gas flow proceeds, counterflow to agglomerates4, from kiln 22 through hood 2] to the preheat chamber 16 where thegases are drawn downwardly through .the bed of agglomerates 4, throughgrate 10 through windbox 18, and through a conduit 32 by a fan 33. Fan33 discharges the gases drawn downwardly through the bed of agglomerates4 in preheat chamber 16, into a conduit 34 that discharges the gasesinto the drying chamber over grate 10. The gases in chamber 15 are drawndownwardly through the bed of agglomerates 4, through grate 10, throughwindbox l7, and through a conduit 35 by a fan 36 which discharges thegases up a stack 37.

The agglomerates 4 are discharged from cooler 30 as heat hardened ballsare discharged to separating and collecting means comprising a secondvibrating screen 40 having a deck 41 with openings sized to pass pelletssmaller than about three-fourths of an inch diameter. Initially, asoperation of the described plant is started, substantially all of thepellets 4 from cooler 30 will pass through deck 41. Screen 40 may alsobe provided with a second deck 42 having openings to collect pelletssmaller than those passing through deck 41 but which are the largerballs within the first size range to provide a predetermined quantity ofballs for a purpose which shall appear as the description of the presentinvention proceeds. The desired quantity of balls may be colshown in US.Pats. Nos. 2,293,439; 2,436,766 or 3,010,145. By adjusting the rates offeed to pan 52 and its angle of inclination, balls may be produced of asize desired for the practice of the present invention, and such ballsare deposited by a second feeder 55, in or preferably on top of the bedon grate 10 which is first formed with balls from balling drum 5, allfor a purpose that will appear from the description of the method ofoperation to follow.

A preferred operation of the apparatus according to the method of thepresent invention will now be described.

Green balls 4 (i.e., unfired) from the first balling device, drum 5, arescreened by screen 6 to provide balls of a first size range ofthree-eighths of an inch to fiveeighths of an inch diameter and formedinto a bed on grate 10. The green balls 4 will be dried in zone 15preheated in zone 16 and given a final burning while tumbling in kiln 22to provide heat hardened pellets of such lected by proper sizing ofopenings in deck 42. For exampl'e, providing a deck 42 with openings offiveeighths of an inch diameter may screen out and collect enough ballsfor the intended purpose, but if not deck 42 may be provided withnine-sixteenths of an inch openings, one-half of an inch openings orwhatever size may be necessary for deck 42 to screen out and collectballs of the quantity desired.

Heat hardened pellets 4 which pass through deck 42 of screen 40 aredischarged to a suitable conveyer 49 for transport to stockpiles.Pellets passing through deck as iron ore. After being cooled in cooler30 the hardened pellets pass to screen 40. Initially, during start-upoperation, substantially all balls will pass through deck 41 of screen40 and on to deck 42. Screen deck 42 is provided with openings sized tocollect from the discharge through deck 41, five-eighths of aninchballs, or if necessary to collect the desired quantity fiveeighthsof an inch balls and nine-sixteenths of an inch balls, from the firstsize range, in order to collect, for example, 1 ton of balls from every30 to 40 tons passing through deck 41. Most of the balls will thereforepass through deck 42 to conveyer 49. The smaller proportion of ballspassing through deck 41 but not through deck 42 are delivered to bin 50.Balls from bin 50 will be rolled in balling pan 52 with finely dividedore from bin 53 to coat the collected balls with ore until they grow insize to a second and larger size range of perhaps about three-fourths ofan inch to 1% inches diameter. These larger balls will be placed uponthe bed of the smaller first size balls from drum 5 which is formed ongrate 10, where the larger balls will be exposed to the hottest gasespassing downwardly therethrough. The coating of the larger balls isdried in zone 15 and preheated in zone 16 along with the drying andpreheating of the smaller size balls in the first formed bed on grate10. The halls of both sizes tumble through kiln 22 wherein the coatingof the large balls and the smaller balls are indurated to achieve thesame desired strength and abrasion resistance. Both size balls passthrough cooler 30 and now with the larger pellets present in the mix,deck 4] screens out the coated balls of the desired larger size anddischarges them to a conveyer 60 for transport to stockpile andspecialized use as for example, a coolant charge to a basic oxygensteelmaking furnace, while the first size range balls pass through deck41 to deck 42 for continued and continuous collection of balls forcoating and production of both the first and second size fully heathardened agglomerate balls for such uses as blast furnace andsteelmaking furnace feeds.

From the foregoing detailed description of the present invention it hasbeen shown how the objects of the present invention have been attainedin a preferred manner. However, modification and equivalents of thedisclosed concepts such as readily occur to those skilled in the art areintended to be included in the scope of this invention. Thus, the scopeof the invention is intended to be limited only by the scope of theclaims such as are or may hereafter be, appended hereto.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A method of making finished fired and heat hardened agglomerates offinely divided mineral ore of a first predetermined desired agglomeratesize and a lesser quantity per unit of time of a second and largeragglomerate size, in a single facility, the method comprising the stepsof:

a. making individual green balls of a first preselected size range fromfinely divided ore;

b. drying, preheating and heat hardening the first size range balls;

c. a first screening of the heat hardened first size range balls toseparate therefrom balls of a preselected size larger than the firstpreselected desired size range when such balls are present and passtherethrough balls within the first preselected size range;

d. a second screening of the heat hardened balls which have passedthrough said first screening to remove during the second screeningpreselected size balls from within the first size range which representless than one half the number of balls that have passed through thefirst screening, and pass through the second screening the remainingsize balls within said first preselected size range which are thencollected for storage as finished fired and hardened agglomerates ofsaid first predetermined desired size;

. rolling the balls removed from the first size range during the secondscreening step, in additional moistened finely divided ore to apply acoating of ore thereto until the rolling balls grow in diameter to apredetermined larger size to provide the balls of said secondpredetermined desired agglomerate size; and

depositing the coated balls with green balls of the first size range fordrying, preheating and final heat hardening of the coating of the coatedballs simultaneously with drying, preheating and final hardening of theballs of the first size range, after which the first said screening stepscreens out the hardened coated balls which are collected to provide thesupply of second desired size agglomerates, and the second screeningcontinues to separate finished fired and hardened agglomerates of thefirst predetermined size from hardened balls of the size prese lectedfor coating.

2. A method according to claim 1 in which the prede termined portion offirst size range balls removed by the second screening for coating is ofthe order of one ton of balls removed for coating from every 30 to 40tons of the total hardened first size agglomerates produeed.

2. A method according to claim 1 in which the predetermined portion offirst size range balls removed by the second screening for coating is ofthe order of one ton of balls removed for coating from every 30 to 40tons of the total hardened first size agglomerates produced.